This invention relates to the art of rotary air motor tools such as screwdrivers, wrenches and in, particular, tools of the described type which incorporate a torque responsive, adjustable, automatic shutoff mechanism.
Various prior art, air powered tools incorporate a torque responsive clutch mechanism which automatically disengages the tool spindle from driving relationship with the motor when the torque increases to a preselected magnitude. Prior art patents which describe such mechanisms include:
______________________________________ Patent No. Inventor Title ______________________________________ 2,732,746 Livermont Torque Limiting Screwdriver 2,984,133 Livermont Torque Limiting Screw Driver 3,020,789 Etzkorn Predetermined Torque Release Hand Tool 3,034,623 Amstberg Hand Clutch Device 3,174,599 Spyridakis, Power Tool Torque Release Clutch et al. Operative In One Direction 3,187,865 Blachowski Predetermined Torque Release Tool With Non-Ratcheting Feature 3,220,526 Gattiker, Jr. One Shot Clutch ______________________________________
Typically, such torque release mechanisms utilize opposed clutch plates which drivingly interconnect by means of bearing members that fit in pockets in the opposed plates. When a predetermined torque level is reached, a biasing force, which normally maintains the plates in driving contact, is overcome and the bearings will move out of the pockets thereby terminating output driving force on the spindle.
Mechanisms of this nature are utilized not only to disengage the driving output from the air motor, but also to effect a shut off device or shut off valve thereby disconnecting the source of pneumatic power to the air tool. For example, Clapp, U.S. Pat. No. 3,515,251 Torque Release and Shut Off Device For Rotary Tools and Frisbie, et al., U.S. Pat. No. 3,262,536 Torque Releasing Clutch Mechanism disclose apparatus for release or closing of an air supply valve upon reaching a predetermined torque. Yet another torque responsive pneumatic tool with an automatic torque responsive shutoff valve is disclosed by Wallace, U.S. Pat. No. 4,071,092, Pneumatic Screwdriver With Torque Responsive Shutoff. Tibbott, U.S. Pat. No. 3,498,389, Automatic Throttle Torque Responsive Power Tool discloses yet another variation of the same type of construction. Another patent which teaches a torque responsive control mechanism for an air tool is Baltz et al., U.S. Pat. No. 4,576,270, Torque Control And Fluid Mechanism For A Fluid Operated Tool.
Often it is desirable initiate operation of such tools by means of a toggle or trigger type switch or a lever control. This is especially true with respect to right angle tools as contrasted with push to start type tools. Thus, various lever mechanisms and trigger mechanisms have been disclosed which are utilized for the initiation of operation of an air motor driven tool by opening the inlet valve to the air motor. Allen, U.S. Pat. No. 3,710,873, Impact Wrench Or Screwdriver; Campbell, et al., U.S. Pat. No. 4,258,798 Air Passages For Pneumatic; States, U.S. Pat. No. 3,741,313, Power Operated Impact Wrench or Screwdriver; States, U.S. Pat. No. 3,578,091, Power Operated Impact Wrench or Screwdriver; Dalton, U.S. Pat. No. 2,899,935, Air Valve for a Pneumatic Tool; and Phisco et al., U.S. Pat. No. 4,024,892, Valve For Use In A Non-installation Tool disclose various types of toggle, trigger, or lever actuated valve mechanisms for initiation of operation of air tools. As previously mentioned certain air tools utilize a push to start mechanism along with a clutch as well as a mechanism to terminate the air flow to the motor of the pneumatic tool. Eckman, U.S. Pat. No. 4,631,992, Screw Driver discloses such a mechanism.
There has remained, however, the need for an improved air driven, rotary vane motor powered tool which includes an adjustable torque responsive clutch mechanism in combination with a valve mechanism that terminates air flow to the air motor upon reaching a predetermined torque level and further which is actuated by a lever actuated or toggle actuated control valve to initially provide fluid for the motor. Utilization of such a mechanism in a right angle screwdriver, for example, or similar pneumatic rotary air motor driven tool would be deemed especially useful. That is, such a tool would operate in response to manual actuation of a lever or trigger to drive a fastener or the like. Upon reaching a predetermined torque level, the clutch of the tool would disengage the air motor from the tool bit and simultaneously would effect closure of the air inlet valve to the air motor. Thereafter, the control lever of the tool, which is typically manually operable, would be released to permit resetting of the tool for the next cycle of operation.